1. Field of the Invention
This invention relates to a camera body, an optical accessory or a camera system.
2. Description of the Related Art
Camera systems of the kind having optical accessories such as an interchangeable lens, an intermediate tube, various converters, etc. detachably mounted on a camera body by a bayonet mount device have been known.
The application of electronics to camera systems has advanced during recent years. As a result, communication and power supply arrangement have become necessary between the camera body and the optical accessory. To meet this requirement, camera systems of varied kinds have been proposed. They have electric connection terminals such as contact pins or the like arranged on both the optical accessory and the camera body. The arrangement is such that: The terminals arranged on both sides come into contact with each other when the optical accessory is mounted on the camera body by rotating the mounts of both sides relative to each other. With the optical accessory thus mounted, the camera body supplies electric energy to the optical accessory and reads the content of a ROM included in the optical accessory or controls actuators disposed within the optical accessory. These camera systems have been disclosed among others in U.S. Pat. Nos. 4,790,649, 4,782,355, 4,924,249, 4,853,725 and 4,999,659; and Ser. No. 913,343 filed on Sept. 30, 1986.
Generally, the power source such as a battery or the like of the camera system is loaded on the camera body and the electric energy is supplied from the camera body to the optical accessory. Therefore, the camera body is provided with power supply terminals including, at least, a power supply level terminal and a ground level terminal.
The power supply terminals of the camera body are hidden and untouchable when the optical accessory is mounted on the camera body. They are, however, exposed to the outside when the optical accessory is not mounted on the camera body. Under that condition, if a metal piece such as a coin or the like is inadvertently brought near to or dropped on the exposed terminals, the metal piece might come into contact with both the power supply level terminal and the ground level terminal. Then, circuits disposed on the side of the camera body might be broken by short-circuit.
To solve this problem, an improvement has been disclosed in U.S. Patent Application Ser. No. 012,862 filed on Feb. 10, 1987. In accordance with this improvement, a switch is arranged on the camera body to effect a power supply to the power supply connection terminal only when the optical accessory is completely mounted on the camera body. This method ensures safety but presents a problem in terms of cost increase.
U.S. Patent Application Ser. No. 221,614 filed on July 20, 1988 has disclosed a method of providing a protruding part near to the electric connection terminals of the optical accessory for the purpose of preventing undesirable things such as dust, etc. from readily coming into contact with the terminals when the accessory is laid down directly on a desk or the like. However, in accordance with that method, the power supply connection terminal on the side of the camera body still remains unprotected from the hazard of short-circuiting.